A four-month-old boy died in Birmingham Children's Hospital after his ventilator failed and the heart and lung bypass machine he was subsequently linked up to was accidentally switched off, an inquest heard yesterday.

Thomas Smith, who had Down Syndrome, was admitted to the hospital in December 2004 for a five-hour procedure for surgery to repair two holes caused by a congenital heart defect. He died five days later.

The inquest was told that after a problem with the ventilator, Thomas was put on a bypass machine but a doctor lifted the lid of the machine, causing it to stop, and how when it was eventually restarted it was put in reverse mode and pumped oxygenated blood into the child.

Doctors had told the boy's mother mother Lisa Weale, of Longbridge, Birmingham, that he was expected to make a full recovery following the heart operation.

She told the inquest he stopped breathing while on the ventilator, less than 24 hours after surgery.

Ms Weale said: "It was thought that everything had gone to plan and that I should go home and for a rest.

"I called the hospital twice to check on him and was advised everything was okay. The next day when I called I was told Thomas was doing very well and they were pleased with his progress."

But the following day, December 11, as the 36-year-old administrator and her partner, Jason Smith, were sat beside their son's cot, they noticed his chest had stopped moving. Ms Weale told the city coroner Aidan Cotter that doctors spent two hours massaging his heart in order to resuscitate him after he suffered a heart attack. He was eventually put on a heart bypass machine, to give his heart a rest.

She said: "The doctor confirmed the ventilator was the problem but didn't know why and couldn't tell me why. They apologised and said they had let Thomas down."

A new doctor was put in charge of her son's care following a shift change on December 12 and he was given a brief run down about how the bypass machine worked.

But a series of errors led to it being inadvertently switched off then restarted in reverse mode.

"At about 10pm on the Sunday, the duty doctor came to do something to the machine. He then lifted the cover which stopped the machine, and he started shouting for help and that he did not know how to restart it," said Ms Weale.

"Later I was told that Thomas may have suffered a stroke as a result of blood being pumped back into his body.

"The medical staff apologised and said they had let Thomas down. They said the doctor in charge was not qualified to operate the bypass machine."

Several attempts were made to try and take her son off the bypass machine but each was unsuccessful as his heart was not strong enough.

Thomas died at Birmingham Children's Hospital at about 4.30pm on December 15, 2004. The cause of death was given as cardiac failure. Dr Duncan Macrae, a consultant paediatrician at the Royal Brompton Hospital in London, was called in by hospital bosses to review Thomas's case notes.

He said a gas leak in the ventilation system had caused the machine to fail, which led the baby to stop breathing and suffer a heart attack.

Dr Macrae said a nurse at his bedside had taken "reasonable action" to remedy the situation by pulling the breathing tube out and checking the lungs were clear of obstructions before reinstating it, but this would not have corrected the fault.

"It's relatively common for some of these tubes to become disconnected. These machines are built to be reliable and have various safety measures but there's always that human element if something goes wrong. A minor abnormality can lead to an horrific chain of events which can cause the heart to stop," he added.

The inquest continues.